The Radio Data System (RDS) enables digital data to be additionally and inaudibly transmitted in parallel with radio programs, in a data channel. Specifications of the Radio Data System for VHF sound radio are defined, inter alia, in the publication Tech. 3244 -E, March 1984 of the European Broadcasting Union (EBU). Besides receiving radio signals, radio receivers having the requisite RDS decoders can receive and decode transmitted data, using the same receiving part. The data transmission takes place in 32 groups of 108 bits each, a specific service being assigned to each group. The group 8a is provided for transmitting digitally coded traffic messages.
The structure and coding of these traffic messages are defined in detail in the proposed standard, ALERT C, November 1990, published by RDS ATT ALERT Consortium. The essential elements of a traffic message are the location of the occurrence and the event. This information is cataloged, i.e., a unique code is assigned to each location and event that have relevance to traffic. The locations are integrated in the location table along existing streets to reproduce the pattern. In addition to the customary receiver devices having an RDS decoder, in order to utilize the traffic report channel TMC (Traffic Message Channel), devices are needed for decoding, storing, further processing, and outputting the traffic messages.
Auto navigators have also become known, which determine the instantaneous position of a vehicle and, with the aid of a digitally stored road map and an entered travel destination, calculate and display proposed routes. To determine position, sensors, which detect the motion of the vehicle on the road surface, as well as satellite positioning systems (GPS) can be used. The calculated routes proposals can be output as maps with the proposed routes marked, or as an instruction on how to proceed at intersections and turn-offs. Thus, auto navigators are known, for example, where an arrow symbol that assumes different shapes and directions shows the motor vehicle driver the way. However, in known auto navigators, the route recommendations and, in some instances, other information are determined merely on the basis of a digitally stored road map, without giving consideration to vicissitudes in the road network, such as temporary irregularities resulting from traffic jams or stoppages.